Most EV’s present the driver with information on how much charge is left in the battery, usually in the form of a percentage. But it turns out, the bar is not necessarily accurate as the car vendor is trying to nudge you into making sensible charging choices, to maximize battery life. While this post will use the specifics from the 2018 Nissan leaf, the principles apply to any EV. For the 2018 Nissan Leaf, we find that 100% state of charge, is actually 90% of rated charge, further the leaf keeps about 4 kWh in reserve, allowing you to go “below” 0 % of displayed state of charge.
Modern EV’s like the 2018 Nissan Leaf use sophisticated battery management systems (BMS). The goal here is for your EV battery to behave in a predictable manner, over the 10-20 year life of your EV. With that in mind, the “operating-range” of your battery will vary between an upper range (shown as 100 % charge) and a lower range (shown as 0 % charge). A reserve at both ends helps ensure the longevity of your battery, how large these are depends on the weather, age and other statistics of your battery.
The 2018 Nissan Leaf does let you use the bottom reserve (see for example this and this), but not the top reserve. Be sure to get familiar with your EV as this may vary depending on the brand. Some EV’s allow you to charge to “completely-full” every once in a while, recommending that you only charge to 80% or so on a routine basis (source, and source). Do note that most trips I do, rarely require a 100% charge.
From my post on battery capacity (see here), we arrived at a 36 kWh usable capacity, while the percent indicator suggested 32 kWh. From these two numbers, the usable reserve at the “bottom” of the battery is about 4 kWh, which is about 20-30 km of driving. This is about half the figure for the equivalent “empty-light” in gas cars, which tends to come on at about 50-90 km (source), but then again, the Leaf yells out a “low-battery-warning” at 10 % displayed charge remaining, which would put it in that range.
In Summary, your EV will nudge you into making sensible charging choices which is usually keeping the state of charge in a range that maximizes your battery life (usually 20%-80% although not always). Be sure to familiarize yourself with your EV, and its battery, to ensure you get many many years of low-emissions adventures out of it.
Electric car adventures 